Identifying affinity-matured human antibodies

Abstract

Antigen-specific immunoglobulin V-regions are identified from a library of nucleic acids amplified using polymerase chain reaction using leader sequence-specific forward primers. The use of leader sequence primers allows all V-region sequences to be amplified (including those with extensive 5′ end mutations) without loss of the original 5′ V gene segment sequence. These libraries can be screened for antigen-specific V-regions using eukaryotic cells engineered to express the amplified V-region-encoding nucleic acids or using bacterial phage display techniques. In the latter, a second V-region library is made using a larger than conventional set of 5′ V-region primers. The sequence errors introduced into the amplification products by this method are corrected using sequence information obtained in the products amplified by the V-region primers to screen the library created using the leader sequence primers. Amino acid sequence information from fragments of donor immunoglobulins can be used to assist in the identification of nucleic acids encoding the heavy and light chains of donor antibodies as well as to design primers to amplify such nucleic acids.

What is claimed is: 
     
       1. A method comprising the steps of:
 (a) using a first PCR to amplify human immunoglobulin heavy and light chain nucleotide sequences from a cDNA library made from a sample of human peripheral blood mononuclear cells obtained from a human donor previously determined to possess antibodies specific for target antigens of interest, wherein a set of leader-specific primers that amplify at least 90% of the human immunoglobulin V region genes used in the PCR amplification; 
 (b) isolating the amplification products from the first PCR step; 
 (c) creating a first set of constructs by inserting the isolated amplification products from the first PCR step into expression vectors; and 
 (d) introducing the first set of constructs into a first set of host cells to create a first library of human immunoglobulin nucleotide sequences. 
 
     
     
       2. The method of  claim 1 , wherein the set of leader-specific primers amplifies 100% of the human immunoglobulin V region genes. 
     
     
       3. The method of  claim 1 , further comprising the step of:
 (e) using a second PCR to amplify human immunoglobulin nucleotide sequences from the first library or the human tissue sample, wherein variable region-specific primers are used in the PCR amplification. 
 
     
     
       4. The method of  claim 3 , further comprising the steps of:
 (f) isolating a second set of amplification products from the second PCR step; 
 (g) creating a second set of constructs by inserting the second set of isolated amplification products into expression vectors; and 
 (h) introducing the second set of constructs into a second set of host cells to create a second library of human immunoglobulin nucleotide sequences. 
 
     
     
       5. The method of  claim 4 , further comprising the steps of:
 (i) screening the second library for a nucleotide sequence that encodes a variable region that specifically binds a target antigen; and 
 (j) obtaining the sequence of the nucleotide sequence that encodes a variable region that specifically binds a target antigen.